Not enough input arguments in function Matlab

Question

I'm having a problem developing my GUI to solve a differential equation and I can not find the error.

The equation I'm trying to solve is defined by:

T*x'+x = kSigma*heaviside(t-t0) + kSin*sin(Omega*t+alpha*pi/180).

The approach I have tried is:

function lsg = DGLvar(t,T,Omega)
   x = 1;
   kSin = 1;
   kSigma = 5;
   t0 = 0;
   alpha = 0;
   lsg = 1/T * (-x + kSigma*heaviside(t-t0) + kSin*sin(Omega*t+alpha*pi/180) );

In the GUI the code looks like this:

function pushbutton1_Callback(hObject, ~, handles)
   t=[0 100];
   periode=get(handles.sliderT,'value');
   Omega=get(handles.slideromega,'value');
   [x,t]=ode45(@DGLvar,t,periode,Omega);
   plot(handles.axes2,x,t,'g')

I'm getting the following error:

Error using DGLvar (line 8)
Not enough input arguments.

Error in odearguments (line 87)
f0 = feval(ode,t0,y0,args{:});   % ODE15I sets args{1} to yp0.

Error in ode45 (line 113)
[neq, tspan, ntspan, next, t0, tfinal, tdir, y0, f0, odeArgs, odeFcn, ...

Error in PT1>pushbutton1_Callback (line 218)
   [x,t]=ode45(@DGLvar,t,periode,Omega);

Error in gui_mainfcn (line 95)
    feval(varargin{:});

Error in PT1 (line 42)
gui_mainfcn(gui_State, varargin{:});

Error in @(hObject,eventdata)PT1('pushbutton1_Callback',hObject,eventdata,guidata(hObject))


Error while evaluating uicontrol Callback

How can I resolve this error?

knedlsepp · Accepted Answer · 2015-01-02 13:36:49Z

3

The solver ode45 expects as input a function f(t,x) and uses this to solve the equation x'=f(t,x).

You need to use x as a parameter for your function DGLvar. I would also recommend renaming it to xprime, as this is more descriptive.

function xp = xprime(t,x,T,Omega)
   kSin = 1;
   kSigma = 5;
   t0 = 0;
   alpha = 0;
   xp = 1/T * (-x + kSigma*heaviside(t-t0) + kSin*sin(Omega*t+alpha*pi/180) );

The GUI code would look like this:

%% Get the GUI values:
tspan = [0 100];
x0 = 0;
T = get(handles.sliderT, 'value');
Omega = get(handles.slideromega, 'value');
%% Define a function with two parameters @(t,x) for ode45.
xprimefixedTandOmega = @(t,x) xprime(t, x, T, Omega);
%% Solve the equation: x' = xprimefixedTandOmega(t,x), x(0)=0 for t=0...100.
[t,x] = ode45(xprimefixedTandOmega, tspan, x0);
%% Plot the result of solver
plot(handles.axes2, t, x, 'g');

edited Jan 2, 2015 at 13:36

answered Jan 2, 2015 at 13:30

knedlsepp

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2 Comments

Henrique Zingg Over a year ago

Thanks for the patience knedlsepp. It worked, but can you please explain me why did you do this: xprimefixedTandOmega = @(t,x) xprime(t, x, T, Omega);

knedlsepp Over a year ago

This line fixes the values T and Omega. Think if You are the solver: "I want to get a function f(t,x). I know the first value is time and the second value is the value at this time. I will then do my magic and return the solution to x' = f(t,x)". When you pass in a function with more then 4 parameters the solver ode45 will think: "Well, I got passed a function with 4 parameters. I know the first is time, the second is the value at this time, but I have no idea what the other two parameters are." Then it tries to use only the first two => Error: "Not enough input arguments."

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